This invention relates to dynamic strobe circuits used in data processors to implement logical functions. A dynamic strobe circuit according to the invention includes an improved dynamic node keeper arrangement that reduces power consumption without significantly affecting circuit performance.
Dynamic strobe circuits are widely used in data processors because of their speed advantage in implementing logical AND functions utilizing a large number of inputs, commonly referred to as xe2x80x9cwidexe2x80x9d AND functions. In particular, dynamic strobe circuits are used in decoders, programmable logic arrays, address comparators, and adders. These processor components or macros are major components of the processor and some are used repeatedly in a single processor.
FIG. 1 illustrates a typical prior art dynamic strobe circuit 100. This prior art dynamic strobe circuit includes a dynamic node 101 connected to a precharge device 102 comprising a P-type field effect transistor (xe2x80x9cFETxe2x80x9d). Dynamic node 101 is also connected to a number of the pull-down devices 103, each comprising a N-type FET. Dynamic strobe circuit 100 also includes a strobe component 104 made up of a P-type FET 105, a N-type FET 106, and an input device 107 which comprises a N-type FET. Devices 105 and 106 each receive a strobe signal S at their respective gate, while input device 107 receives the signal present on dynamic node 101. The signal at the dynamic node represents the input to strobe component 104, while the output of the strobe component is taken at the junction between P-type device 105 and input device 107. This strobe component output is connected to an intermediate node or strobe dynamic node 108. The signal at intermediate node 108 is inverted by inverter 109 and applied as the output of the dynamic strobe circuit at circuit output node 110. This output signal is fed back to control an output keeper device, P-type FET 111.
The prior art strobe circuit shown in FIG. 1 includes a keeper arrangement 112 for dynamic node 101. This prior art keeper arrangement 112 includes an inverter 114 connected to receive the signal at dynamic node 101, and to apply the inverted signal to control a keeper device, P-type FET 115. A drawback of this prior art keeper arrangement 112 is that keeper device 115 is on or active any time dynamic node 101 is at a logical high voltage level. Thus, keeper device 115 is normally conductive and dissipating power, even during the precharge period.
A dynamic strobe circuit according to the invention includes an improved dynamic node keeper arrangement. The improved dynamic node keeper arrangement includes a keeper device that is controlled by the signal at the intermediate node, that is, the signal at the output of the strobe component. By controlling the dynamic node keeper device through the strobe component output, the keeper device is active or conductive only when necessary to protect against noises in the pull-down network. At all other times in the course of operation of the dynamic strobe circuit, the dynamic node keeper device according to the invention is nonconductive or inactive. Thus, the dynamic strobe circuit according to the invention reduces power consumption. The present dynamic node keeper arrangement also eliminates the inverter required to provide the control signal in the prior art keeper arrangement, and thus reduces the number of devices in the circuit. These benefits are obtained without any significant impact on circuit performance.
The invention includes a method for controlling the dynamic node of a dynamic strobe circuit to decrease power consumption in the circuit. The method includes first precharging the dynamic node of the circuit during a precharge period, and then selectively connecting the dynamic node to the supply voltage through the keeper device in response to, or under the control of, the strobe component output. Controlling the dynamic node keeper device by the strobe component output ensures that the keeper device is in its conductive state, and thus dissipating power, only when necessary to protect the dynamic node from spurious signals to the draw-down devices.
These and other objects, advantages, and features of the invention will be apparent from the following description of the preferred embodiments, considered along with the accompanying drawings.